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calculating injector flow requirements

1512 Views 4 Replies 3 Participants Last post by  dzlhead, 
D
I am new to this site, and after reading some of the faq's about the various injector options, is there a mathematical formula that shows the correlation between fuel flow (injector and pump in cc's) and horsepower production?
I have been doing the math for a project that I am working on, yet when it comes to getting the equations for the fuel side it has been hard going. Call the fuel injection shops and it seems that it's secret code or something.
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chittychittybangbang
I believe there are too many factors to make an accurate formula. A better forumla would be to estimate the fuel flow at a certain pressure and temperature. Gas engines have formulas that estimate fuel flow and hp production but again, they are estimates only.

Here's a start: http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html
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Shouldn't the max fuel flow be constant for each pump? The pump can only flow so much fuel.
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chittychittybangbang
On second thought, fuel flow as volume is OK because fuel mass and temp roughly equal pressure.

If it's OK to use gasoline information, here are some more sources. Diesel isn't quite the same because the Bosch VW pumps operate like a pressure wave. In terms of fuel flow per injector, my best guess is that the newer common rails operate more like gasoline engine fuel injectors because they are releasing fuel out of a common pressurized rail. The difference is that the new TDI common rail is 20,000-28,000psi vs. a traditional gasoline fuel injection system of about 60-80 psi.

http://www.rceng.com/technical.aspx

I don't know what the duty cycle of the newest TDI injector is and I don't think that is even applicable because the duty cycle is a % time the solenoid opens the injector. The older TDIs just opened in response to a pressure wave, the newer TDI used a solenoid, the newest use a piezoelectric crystal to inject fuel. But hopefully this will get you started!
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chittychittybangbang said:
On second thought, fuel flow as volume is OK because fuel mass and temp roughly equal pressure.

If it's OK to use gasoline information, here are some more sources. Diesel isn't quite the same because the Bosch VW pumps operate like a pressure wave. In terms of fuel flow per injector, my best guess is that the newer common rails operate more like gasoline engine fuel injectors because they are releasing fuel out of a common pressurized rail. The difference is that the new TDI common rail is 20,000-28,000psi vs. a traditional gasoline fuel injection system of about 60-80 psi.

http://www.rceng.com/technical.aspx

I don't know what the duty cycle of the newest TDI injector is and I don't think that is even applicable because the duty cycle is a % time the solenoid opens the injector. The older TDIs just opened in response to a pressure wave, the newer TDI used a solenoid, the newest use a piezoelectric crystal to inject fuel. But hopefully this will get you started!
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This is actually a good start, since using the formulae from the Garrett site offers the BSFC numbers and A/F ratios when calculating the airflow requirements and boost requirements. Should a percentage be added for the difference in the btu content of the fuel and should you adjust for max power A/F ratio for diesel? Gas is like 12-13 to 1 for best power while diesel is like 10 to 1. Thanx again for the responses.:thumbsup
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